1. Technical Field of the Invention
The present invention relates to a valve controller and a valve controlling method, and more particularly to a device and the like for controlling valve opening of a motor-driven valve for adjusting the quantity of refrigerant and others.
2. Description of the Related Art
Motor-driven valves are adaptable for various kinds of usage such as expansion valves for controlling the quantity of refrigerant in refrigeration cycles. PID control used for controlling valve opening of the motor-driven valve also is, as disclosed in Patent document 1, a controlling method for obtaining an operation amount (opening of motor-driven valve) through calculation by substituting control parameters (PID coefficients) determined by the system and load where the controlling method is applied and so on, that is, a proportional band PB (proportional coefficient Kp), an integral time Ti, a differential time Td and a deviation between temperature of controlled object (degree of superheat) and target temperature (target degree of superheat) to an arithmetic expression for control with proportional term, integral term and differential term.
Further, the control parameters (PID coefficients) were required to be changed in magnitude in accordance with the system and load to obtain the optimum temperature control performance, and abundant experience and expert knowledge were required to manually set the parameters. Therefore, the parameters have been set by a skillful user with long-term experience based on a trial-and-error technique through test run with actual device or the like for a long period of time while repeatedly performing variety of patterns. From this viewpoint, in recent years, as disclosed in Patent documents 1 and 2, automatic tuning functions for automatically setting the control parameters were developed, with the functions, it became possible for even users without abundant experience and expert knowledge to relatively easily set the control parameters.    [Patent document 1] Japanese Patent Publication Showa 58-68107 gazette    [Patent document 2] Japanese Patent Publication 2000-155603 gazette